Dimerisation of nitrile oxides: A quantum-chemical study

Tibor Pasinszki, Balázs Hajgató, Balázs Havasi, Nicholas P.C. Westwood

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The [3 + 2] and [3 + 3] cyclodimerisation processes of small nitrile oxides, XCNO (X = F, Cl, Br, CN, CH3) are investigated by ab initio coupled cluster theory at the CCSD, CCSD(T) and MR-AQCC levels for the first time. The favoured dimerisation process is a multi-step reaction to furoxans (1,2,5-oxadiazole-2-oxides) involving dinitrosoalkene-like intermediates with diradical character. The rate determining step for all but the F-species is the first, corresponding to the C-C bond formation. The kinetic energy barrier depends on the nature of the substituent X, generally increasing with decreasing electronegativity and increasing π-donor ability of the substituent: F (ΔG298 = 0 kJ mol-1) < Cl (72) < Br (90) < CH3 (104) < CN (114) (MR-AQCC(2,2)//UB3LYP/cc-pVTZ). Following initial C-C bond formation, three possible dinitrosoethylene diradical pathways are explored. Two of them are new, and one of them is a low-energy three-step path with implications for cycloreversion, tautomerism and detection of dinitrosoethylene intermediates. Alternative one-step, concerted [3 + 2] and [3 + 3] cyclodimerisation processes leading to 1,2,4-oxadiazole-4-oxides and 1,4,2,5-dioxadiazines have kinetic energy barriers around 100-240 kJ mol -1 (CCSD//B3LYP), some 1.6 to 2.5 times higher than those leading to furoxans, supporting the experimental observations of furoxan formation as nitrile oxide loss channels during storage, trapping/re-vaporisation and reactions of nitrile oxides. Potential polymerisation initiation processes for NCCNO, involving the 1,2-dipolar NC substituent are also explored.

Original languageEnglish
Pages (from-to)5263-5272
Number of pages10
JournalPhysical Chemistry Chemical Physics
Issue number26
Publication statusPublished - Sep 28 2009


ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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